N-Tox® is a patented nitrification toxicity monitoring system that provides early warning of activated sludge failure and consequent wastewater treatment works breakdown, and helps prevent ammonia pollution of the aqueous environment.

The product detects nitrous oxide (N2O), a harmful greenhouse gas with global warming potential almost 300 times that of carbon dioxide.

The unique features of N-Tox® include:

  • critical early-warning device, used to monitor nitrification effectiveness in municipal and industrial activated sludge systems;
  • real time response allowing proactive management by providing an earlier warning compared to other systems because the indicator of the failure of the treatment process, N2O, is produced instantaneously;
  • robust, non-invasive technique based on gas-phase detection which avoids sampling of activated sludge and eliminates associated probe fouling and maintenance issues;
  • simple, low cost technology requires minimal operator intervention and utilises a proven, standard N2O detector;
  • innovative design comprises an integral sample pump, gas conditioning device, non-dispersive IR gas analyser, auto-calibration system and data logging unit, housed within an IP65 enclosure;
  • no expensive consumables such as chemical reagents or calibration standards.

How it Works

Prior research at Cranfield University has demonstrated that nitrogen oxide (N2O) is rapidly detected when nitrification starts to fail. The rate of N2O production is linked to oxygen depletion, presence of toxic substances and ammonia shock loadings. Increases in levels are directly related to nitrification failure. Hence, measurement of the N2O off-gas level allows the monitoring of nitrification performance to prevent breakthrough of ammonia in final effluent.


Using N-Tox® to detect an increase of N2O above the start of an activated sludge aeration lane or a trickling filter means that at least one hydraulic retention time of the final clarifier would pass before nitrification failure. The graph below demonstrates that the time lag between detection of increased N2O and the appearance of ammonia provides typically seven hours warning of nitrification failure.

Once a failure is detected, plant operators and asset managers can implement a number of process options to restore nitrification including increasing aeration rates, bypassing influent to storage tanks, recycling final effluent to works inlet, or controlling return of high ammonia sludge liquors.


N-Tox® can be used to monitor any activated sludge system in either municipal sewage or industrial effluent treatment systems. Many treatment works that discharge direct to the aqueous environment are consented for ammonia at < 5 mg/l as NH3-N. These plants rely on ammonia removal through bacterial conversion to nitrate.

Inhibition by aeration failure, toxic chemicals or high ammonia concentrations can result in a wastewater treatment works not meeting its required ammonia consent. Some industrial effluents, such as landfill leachate or pharmaceutical wastewaters, have high ammonia levels. The requirement for an N-Tox® alarm here is critical as the consequences of nitrification failure are more serious.

N-Tox® can also be used to quantify N2O greenhouse gas emissions from wastewater treatment plants. This is an area of increasing concern to plant operators and regulators alike, due to the particular potency of N2O as a geeenhouse gas.

N-Tox® Equipment Specification



Gas Type:

N2O (nitrous oxide, dinitrogen oxide)

Measuring Method:

Non dispersive IR absorption

Measuring Limit:

100-2000ppm  N2O (speicified by user)


0.1-1 ppm N2O (dependant on the scale)


+/- 1% of the scale

Lower Detection Limit:

0.2-2 ppm N2O (dependant on the scale)

Cross Sensitivity:

1 ppm N2O per 1000/30,000 ppm CO2 (depending on model)

Response Time:

8 - 30 seconds (dependent gas-sample line length)

Monitoring Interval:

1 second

Operating Temperature:

0 - 50°C

Relative Humidity:

0-100% RH, non-condensing (at operating temperature)




Continuous single-point monitoring

Sample Gas Conditioning:

Gas filter + semi-permeable membrane dryer

Offset & Drift Compensation:

Auto drift compensation


Factory set with auto adjustment for temperature drift, IR source aging and pressure changes


Electrical & Compliance Data

Power Supply:

110 - 240 VAC, 50/60 Hz

Power Consumption:

0.150 kW

Max Current:

1.2 A


Enclosure Details

Ingress Protection:



Glass Fibre


height 647mm, width 430mm, depth 250mm




1/4" (6.35mm) pipe fittings

Tube Material:

PTFE or Nylon tubing


Maximum tube length 15m

Gas collection hood:

Floating gas collection hood supplied with the unit

Data Display, Inputs & Outputs


LCD screen display

Data Presentation:

3 main operating screens, numerical data, alarm history, & test screen

Data Storage:

Data stored using flash memory card (1 minite intervals, daily file packets)

Analogue Output:

4 - 20 mA current loop (utilised by Datalogger)

Alarm Signals:

Low level and high level alarms (user defined), and fault alarm

Computer Interface:

Webpage generate that can be accessed via ethernet cable or an internal modem


For further details please contact:

Water Innove Ltd
Building 45 (CUBIC)
Cranfield University, Cranfield
Bedfordshire, UK
MK43 0AL

Tel. +44 (0) 1234 758054
Fax. +44 (0) 1234 758051

Email This email address is being protected from spambots. You need JavaScript enabled to view it.

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